(1) Field of the Invention
The invention relates to the fabrication of integrated circuit devices, and more particularly, to a method of repairing high-end quartz masks.
(2) Description of the Prior Art
One of the most essential components that is used during the process of performing photolithographic exposures is a photomask that contains patterns that need to be transposed from the mask to underlying layers of semiconductor material such as most notably the surface of a layer of photoresist. The standard mask comprises a transparent substrate on the surface of which a patterned layer of opaque material has been created. Typically used for the opaque material is chromium that has been deposited over the quartz substrate to a thickness of about 1,000 Angstroms.
Alternate opaque materials for the creation of the patterned layer on the surface of a photolithographic mask are nickel and aluminum. For the substrate quartz is typically used, however glass and sapphire can also be used for this purpose.
More sophisticated photo masks apply the principle of phase shifting of the light as the light passes through the mask for the purpose of creating device features of sub-micron dimensions. In these Phase Shifting Masks (PSM) the projected light that is in extreme close physical proximity is mutually interactive, having a detrimental effect on the definition of the exposed pattern.
As a further advance, alternate phase shifting masks can be used, where the phase shifting characteristic of the phase shifting mask is alternately applied to the light as the light passes through the photo mask. A further level of sophistication is introduced by the use of regions on the substrate of the photomask that pass light in a graded manner. The light that passes through the mask can in this case be controlled so that not only complete passing or complete blocking of light takes place but that the mask also provides a graded exposure. This graded exposure may for instance be of use in creating dual damascene structures, where depth of light exposure can be used for non-uniform removal of a layer of photoresist over the thickness of the layer of photoresist.
The photolithographic mask is created using conventional methods of depositing (including sputtering) a layer of opaque material over a surface of the substrate of the mask and patterning this layer using conventional high resolution methods of exposure such as E-beam exposure. Due to the frequently used high density of the pattern that is developed in the layer of opaque material, this formation is exposed to a number of problems that result in bad and unusable masks.
These masks are frequently repaired, based on a cost analysis as to whether it is best (most cost effective) to repair the mask or whether it is best to scrap the defective mask.
Defects that can occur in the creation of an opaque pattern over the surface of a substrate are opaque material remaining in place where it should be removed and visa versa, the formation of an interconnect or bridge between closely spaced adjacent lines of the opaque pattern, extensions of the opaque material into transparent surface regions of the mask, the occurrence of an isolated opaque spot in a transparent region and visa versa, the formation of pin holes in either the opaque or the transparent surface area and the like.
A number of methods have been provided for the repair of photo masks. In view of the density and the potential complexity of the pattern that has been created on the substrate of the photo mask, this process however can be cumbersome, time consuming and expensive. The invention provides a method that is reliable and can be readily made part of a semiconductor manufacturing environment.
U.S. Pat. No. 6,190,836 B1 (Grenon et al.) discloses a method for repairing a photomask.
U.S. Pat. No. 6,103,430 (Yang) reveals a method to repair a PSM.
U.S. Pat. No. 5,965,301 (Nara et al.) shows a method to remove a residual defect in a mask.
U.S. Pat. No. 5,965,303 (Huang) shows another PSM repair method.